1. Field of the Invention
The present invention relates generally to an apparatus for protecting a welding position detector which is attached to an extreme end of a multi-articulated type industrial robot, i.e., an arc-welding robot, to detect an arc-welding position on a workpiece welded by an arc-welding torch attached to the extreme end of the arc-welding robot. More particularly, it relates to a cooling and cleaning apparatus for preventing a sensor unit sealably encased in the housing arc-welding position of the welding position detector from being damaged by heat generated at welded positions to the workpiece and from contamination by fumes and welding-sputter during welding.
2. Description of the Related Art
Arc-welding robots are frequently used in the field of manufacturing and assembling automobiles and of assembling structural elements of buildings, and arc-welding robots are constructed as a multi-articulated type industrial robot having a robot wrist on which an arc-welding torch and an arc sensor are mounted. The arc sensor of an arc-welding robot detects welding positions along a desired welding line on a workpiece, and sends the detected data to a robot controller. Thus, the robot controller controls the motion of the moving elements of the arc-welding robot according to the detected data to thereby transfer the arc-welding torch to an objective position suitable for applying arc-welding to the detected welding positions of the workpiece along the desired welding line. Nevertheless, the arc sensor has recently been modified into a different type arc-welding position sensor referred to as an optical arc-welding position detector which can be mounted on the conventional arc-welding robot in the same manner as the arc sensor.
The optical arc-welding position detector mounted on the arc-welding robot is provided with a light-emitting element in the form of a semi-conductor laser arranged so as to emit a laser beam illuminating the surface of the welded workpiece, and a light-receiving element in the form of a charge-coupled device (CCD) arranged so as to receive the laser beam when it is reflected by the surface of the workpiece to thereby obtain data of the configuration of the workpiece surface on the basis of the received laser beam. This type of arc-welding position detector is also provided with a casing for containing therein the above-mentioned sensor unit including the semiconductor laser, an objective lens element, an assembly of a galvanometric device and a mirror for providing the emitting laser with scanning action against the surface of a welded workpiece, the light-emitting element in the form of the CCD, and a light-receiving lens element. The casing of the arc-welding position detector is covered with a window made of a transparent resin material and the like, in order to protect all of the above-mentioned sensor unit from contamination by the fumes and welding-sputter during the arc-welding operational.
When the optical welding-position detector is used with the arc-welding robot for, for example, welding either ceiling portions in the interior of each vehicle body in a car assembling station or high corner portions of metallic frameworks of a building at a building site, a problem occurs that the above-mentioned protective window of the arc-welding position detector is unavoidably contaminated by attachment or deposition of welding-sputter resulting in making it impossible to emit a detecting laser beam and to receive the laser beam reflected from the welded positions. Namely, when the arc-welding robot must be used in such a position and posture that the welding torch and the protective window of the arc-welding position detector are positioned so as to be directed upward, the welding fume and the welding-sputter fall down and are attached to or deposited onto the face of the window of the arc-welding position detector during the welding operation of the robot. Thus, the arc-welding position detector using the laser beam as a position detecting medium cannot achieve accurate detection of the welding positions on the surface of the workpiece.
In order to solve the above-mentioned problem, Japanese Unexamined Patent Publication (Kokai) No. 6-91586 filed by the same assignee as the present U.S. Patent application has already disclosed a proposal for cleaning the window of the arc-welding position detector by supplying pressurized gas, preferably pressurized air, to the face of the window. The pressurized air cleans the external face of the window of the arc-welding position detector and forms an external air-curtain covering and protecting the external face of the window.
Nevertheless, the sensor unit, i.e., the semiconductor laser, the CCD type light-receiving element, and the other electronic and optical elements encased in the outer casing of the welding-position detector are not durable against heat. Therefore, an arrangement of an appropriate cooling means for cooling the above-mentioned sensor unit encased in the outer casing of the welding-position detector is indispensable for enhancing the thermal durability of the detector to thereby increase the operation life and accuracy in the detection of the welding position.
In order to effectively cool the encased electronic and optical elements including the semiconductor laser and the CCD type light-sensing element, it is necessary to supply a flow of cooling gas, particularly a cooling air, into the interior of the casing of the welding-position detector so as to directly remove heat from the electronic and optical elements. However, if both the formation of the above-mentioned external curtain and the supply of the cooling air are individually implemented by using independent flows of gas, two separate gas supply systems and various flow control valves are needed, and accordingly, it is impossible to simplify the peripheral arrangement of the optical welding-position detector and to reduce the size of the optical welding-position detector. As a result, the optical welding-position detector must suffer from an inconvenience that the detector is unable to detect welding positions located in a narrow region of a welded object such as an interior of a vehicle body.